Linearity is important for reducing interference and crosstalk between signals for both transmit and receive applications. Achieving high linearity becomes particularly difficult for emerging applications that seek large bandwidth, high power, and high efficiency simultaneously. As such, these demands are difficult to accomplish through circuit linearization techniques alone.
Presently, FETs are generally inferior to heterojunction bipolar transistors (HBTs) in linearity performance. However, FETs have better power handling capability. Therefore, a FET with improved linearity is desirable. This method is expected to improve the power ratio of carrier (C) to intermodulation (I) signal (C:I) by 5-10 dB for AlGaN/GaN FETs.
For AlGaN/GaN heterostructure field effect transistors (HFETs), techniques used in the state of the art to improve linearity have significant drawbacks. Increasing the barrier thickness: 1) will reduce transconductance (gm) and high frequency performance; 2) a two-channel structure will reduce breakdown voltage; and 3) introducing Al into a GaN channel could reduce mobility and gm.
Thus, it is desirable to provide embodiments of a FET device and method for making same that are able to overcome the above disadvantages in order to increase linearity without degrading breakdown voltage or frequency performance, and with a small impact on peak gm.